This invention relates to ad-hoc networks, especially to a self-configuring wireless sensor network operating in multipath-rich indoor areas, and to a method for organizing such network.
There has been an increase in the use of ad-hoc wireless sensor networks for monitoring environmental information (temperature, pressure, mineral content, sound levels, light etc) across an entire physical space. The sensor data from these sensors may only be useful if the location they refer to is known with sufficient precision. Position data can be obtained from Global Positioning System (GPS) data which, however, is a very expensive solution to this requirement. Instead, techniques to estimate sensor/node positions are being developed that rely just on the measurements of distances between neighboring nodes. The distance information could be based on such criteria as time of arrival, time-difference of arrival and received signal strength. Depending on the accuracy of these measurements, processor power and memory constraints at each of the nodes, there is some degree of error in the distance information.
The precision with which the location of a sensor can be determined tends to increase with the number of nodes near the sensor that have a known position. In many situations, however, only the positions of a few anchor nodes are known which were previously determined using, for example, GPS data. Position determination required to locate, for example, emergency response personnel inside a building needs to be quite accurate in order to provide assistance in the event of impending danger.
It would therefore be desirable to add, preferably automatically, additional trusted nodes, i.e., nodes whose location is known, to an ad-hoc network, which can then be used to allow a more accurate position determination of sensors.